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.TH "MPI_IMRECV" "3" "May 30, 2025" "" "Open MPI"
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.sp
\fI\%MPI_Imrecv\fP — Non\-blocking receive for a matched message
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

int MPI_Imrecv(void *buf, int count, MPI_Datatype type,
     MPI_Message *message, MPI_Request *request)
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq
MPI_IMRECV(BUF, COUNT, DATATYPE, MESSAGE, REQUEST, IERROR)
     <type>  BUF(*)
     INTEGER COUNT, DATATYPE, MESSAGE, REQUEST, IERROR
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE mpi_f08
MPI_Imrecv(buf, count, datatype, message, request, ierror)
     TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buf
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Message), INTENT(INOUT) :: message
     TYPE(MPI_Request), INTENT(OUT) :: request
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBcount\fP: Number of elements to receive (nonnegative integer).
.IP \(bu 2
\fBdatatype\fP: Datatype of each send buffer element (handle).
.IP \(bu 2
\fBmessage\fP: Message (handle).
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBbuf\fP: Initial address of receive buffer (choice).
.IP \(bu 2
\fBrequest\fP: Request (handle).
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
The functions \fI\%MPI_Mrecv\fP and \fI\%MPI_Imrecv\fP receive messages that have been
previously matched by a matching probe.
.sp
The \fIrequest\fP returned from \fI\%MPI_Imrecv\fP can be used with any of the
\fI\%MPI_Test\fP and \fI\%MPI_Wait\fP variants, like any non\-blocking receive request.
.sp
If \fI\%MPI_Imrecv\fP is called with \fBMPI_MESSAGE_NULL\fP as the message argument, a
call to one of the \fI\%MPI_Test\fP or \fI\%MPI_Wait\fP variants will return immediately
with the \fIstatus\fP object set to \fIsource\fP = \fBMPI_PROC_NULL\fP, \fItag\fP =
\fBMPI_ANY_TAG\fP, and \fIcount\fP = 0, as if a receive from \fBMPI_PROC_NULL\fP was
issued.
.sp
If reception of a matched message is started with \fI\%MPI_Imrecv\fP, then it is
possible to cancel the returned request with \fI\%MPI_Cancel\fP\&. If \fI\%MPI_Cancel\fP
succeeds, the matched message must be found by a subsequent message
probe (\fI\%MPI_Probe\fP, \fI\%MPI_Iprobe\fP, \fI\%MPI_Mprobe\fP, or \fI\%MPI_Improbe\fP), received by a
subsequent receive operation or canceled by the sender.
.sp
Note, however, that is it possible for the cancellation of operations
initiated with \fI\%MPI_Imrecv\fP to fail. An example of a failing case is when
canceling the matched message receive would violate MPI message ordering
rules (e.g., if another message matching the same message signature has
matched — and possibly received — before this \fI\%MPI_Imrecv\fP is canceled).
.sp
If your application does not need to examine the \fIstatus\fP field, you
can save resources by using the predefined constant
\fBMPI_STATUS_IGNORE\fP as a special value for the \fIstatus\fP argument.
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler associated
with the communication object (e.g., communicator, window, file) is called.
If no communication object is associated with the MPI call, then the call is
considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
handler is called for all other MPI functions.
.sp
Open MPI includes three predefined error handlers that can be used:
.INDENT 0.0
.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP was called
on a communicator containing the group of processes in the
corresponding window or file. If called on a session,
aborts only the local process.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
.UNINDENT
.sp
MPI applications can also implement their own error handlers by calling:
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
.UNINDENT
.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.sp
Note that per the “Return Status” section in the “Point\-to\-Point
Communication” chapter in the \fI\%MPI Standard\fP, MPI errors on messages received
by \fI\%MPI_Imrecv\fP do not set the \fBstatus.MPI_ERROR\fP field in the
returned \fIstatus\fP\&.  The error code is always passed to the back\-end
error handler and may be passed back to the caller through the return
value of \fI\%MPI_Imrecv\fP if the back\-end error handler returns it.
The pre\-defined MPI error handler \fBMPI_ERRORS_RETURN\fP exhibits this
behavior, for example.
.sp
\fBSEE ALSO:\fP
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.INDENT 3.5
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Mprobe\fP
.IP \(bu 2
\fI\%MPI_Improbe\fP
.IP \(bu 2
\fI\%MPI_Probe\fP
.IP \(bu 2
\fI\%MPI_Iprobe\fP
.IP \(bu 2
\fI\%MPI_Imrecv\fP
.IP \(bu 2
\fI\%MPI_Cancel\fP
.UNINDENT
.UNINDENT
.UNINDENT
.SH COPYRIGHT
2003-2025, The Open MPI Community
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